Microtubule cytoskeleton perturbation induced by taxol and colchicine affects chaperonin containing TCP-1 (CCT) subunit gene expression in Tetrahymena cells

Possible involvement of CCT5, RGS3, and YKT6 genes up-regulated in p53-mutated tumors in resistance to docetaxel in human breast cancers

BACKGROUND

Present study was aimed to investigate the relationship of p53 mutation status with response to docetaxel in breast cancers. In addition, attempts were made to identify the genes differentially expressed between p53-wild and p53-mutated breast tumors and to study their relationship with response to docetaxel.

METHODS

Mutational analysis of p53 was done in 50 breast tumor samples obtained from primary breast cancer patients (n = 33) and locally recurrent breast cancer patients (n = 17) before docetaxel therapy. Response to docetaxel was evaluated clinically. Gene expression profiling (n = 2,412) was conducted by adapter-tagged competitive-PCR in 186 tumor samples, which were also analyzed in their p53 mutational status in order to identify the differentially expressed genes according to p53 mutation status and their relationship with response to docetaxel.

RESULTS

Response rate of p53-mutated tumors (44%) was lower than that of p53-wild tumors (62%) though there was no statistical significance (P = 0.23). Of 2412 genes, mRNA expression of 13 genes was significantly different between p53-wild and p53-mutated tumors. Of these 13 genes, mRNA expression of CCT5, RGS3, and YKT6 was significantly up-regulated in p53-mutated tumors and associated with a low response rate to docetaxel. Treatment of MCF-7 cells with siRNA specific for CCT5, RGS3, or YKT6 resulted in a significant enhancement of docetaxel-induced apoptosis.

CONCLUSIONS

CCT5, RGS3, and YKT6 mRNA expressions, which are up-regulated in p53-mutated breast tumors, might be implicated in resistance to docetaxel and clinically useful in identifying the subset of breast cancer patients who may or may not benefit from docetaxel treatment.

Multiple tubulin forms in ciliated protozoan Tetrahymena and Paramecium species

Tetrahymena and Paramecium species are widely used representatives of the phylum Ciliata. Ciliates are particularly suitable model organisms for studying the functional heterogeneity of tubulins, since they provide a wide range of different microtubular structures in a single cell. Sequencing projects of the genomes of members of these two genera are in progress. Nearly all members of the tubulin superfamily (alpha-, beta-, gamma-, delta-, epsilon-, eta-, theta-, iota-, and kappa-tubulins) have been identified in Paramecium tetraurelia. In Tetrahymena spp., the functional consequences of different posttranslational tubulin modifications (acetylation, tyrosination and detyrosination, phosphorylation, glutamylation, and glycylation) have been studied by different approaches. These model organisms provide the opportunity to determine the function of tubulins found in ciliates, as well as in humans, but absent in some other model organisms. They also give us an opportunity to explore the mechanisms underlying microtubule diversity. Here we review current knowledge concerning the diversity of microtubular structures, tubulin genes, and posttranslational modifications in Tetrahymena and Paramecium species.

CCTeta, a novel soluble guanylyl cyclase-interacting protein

Nitric oxide (NO) transduces most of its biological effects through activation of the heterodimeric enzyme, soluble guanylyl cyclase (sGC). Activation of sGC results in the production of cGMP from GTP. In this paper, we demonstrate a novel protein interaction between CCT (chaperonin containing t-complex polypeptide) subunit eta and the alpha1beta1 isoform of sGC. CCTeta was found to interact with the beta1 subunit of sGC via a yeast-two-hybrid screen. This interaction was then confirmed in vitro with a co-immunoprecipitation from mouse brain. The interaction between these two proteins was further supported by a co-localization of the proteins within rat brain. Using the yeast two-hybrid system, CCTeta was found to bind to the N-terminal portion of sGC. In vitro assays with purified CCTeta and Sf9 lysate expressing sGC resulted in a 30-50% inhibition of diethylamine diazeniumdiolate-NO-stimulated sGC activity. The same assays were then performed using BAY41-2272, an NO-independent allosteric sGC activator, and CCTeta had no effect on this activity. Furthermore, CCTeta had no effect on basal or sodium nitroprusside-stimulated alphabeta(Cys-105) sGC, a constitutively active mutant that only lacks the heme group. The N-terminal 94 amino acids of CCTeta seem to be critical for the mediation of this inhibition. Lastly, a 45% inhibition of sGC activity by CCTeta was seen in vivo in BE2 cells stably transfected with CCTeta and treated with sodium nitroprusside. These data suggest that CCTeta binds to sGC and, in cooperation with some other factor, inhibits its activity by modifying the binding of NO to the heme group or the subsequent conformational changes.

Morphological and physiological changes in Tetrahymena pyriformis for the in vitro cytotoxicity assessment of Triton X-100

Non-ionic surfactants such as Triton X-100 have been widely used in industrial processing and in cleaning products for almost 50 years, being effective and economic emulsifying, wetting agents, dispersants and solubilizers. Cleaning products containing these surfactants are disposed of mainly by discharge into wastewater, which receives biological treatment in wastewater treatment systems. However, surface-active agents interact with eukaryotic cell membranes leading to biological damage at high concentrations. Tetrahymena pyriformis was used here as model organism to assess the effects of Triton X-100 through a series of in vitro cytotoxicity tests. Growth rates and morphological changes were, by their simplicity and reproducibility, the simplest toxicological assays. Cytoskeleton analysis seemed to be related with phagocytosis rate. Viability was evaluated by two different tests. Calcein AM/EthD-1 was used to assess T. pyriformis membrane damage during the 48-h experiment. The colorimetric MTT assay proved to be highly sensitive even at very short periods of Triton X-100 exposure. Tests performed in this study included simple and fast bioassays that provide overall information on the morphological and physiological state of cells exposed to different non-lytic and lytic concentrations of Triton X-100.

Function and regulation of cytosolic molecular chaperone CCT

Molecular chaperones are a group of proteins that assists in the folding of newly synthesized proteins or in the refolding of denatured proteins. The cytosolic chaperonin-containing t-complex polypeptide 1 (CCT) is a molecular chaperone that plays an important role in the folding of proteins in the eukaryotic cytosol. Actin, tubulin, and several other proteins are known to be folded by CCT, and an estimated 15% of newly translated proteins in mammalian cells are folded with the assistance of CCT. CCT differs from other chaperonin family proteins in its subunit composition, which consists of eight subunit species comprising the CCT 16-mer double-ring-like complex. CCT preferentially recognizes quasinative (or partially folded) intermediates, whereas its Escherichia coli homologue GroEL recognizes more unfolded intermediates, especially those displaying hydrophobic surfaces. Molecular evolutionary analyses have suggested that each subunit species has a specific function in addition to contributing to a common ATPase activity. Consistent with this view, it has been suggested that each subunit recognizes specific substrate proteins (or their parts) and that they collectively modulate the ATPase activity of the complex. The overall expression of CCT in mammalian cells is primarily dependent on cell growth, but each subunit exhibits an individual patterns of expression. Recent progress in CCT research is reviewed, focusing particularly on CCT function and expression. From these observations, the possible roles of the distinct subunits in CCT-assisted folding in the eukaryotic cytosol are discussed.